The present invention relates to a new and improved method for producing a perforated body for receiving textile fibers or fibrous material deposited on a fiber receiving surface of the perforated body by means of an airstream. The perforated body is advantageously used in a friction spinning means or element which, in turn, is used in a friction spinning device.
Friction spinning means or elements as described are used in a known friction spinning method or process in which usually the friction spinning means or elements comprise two cylindrical spinning drums arranged next to each other and rotating in the same direction. At least one of the two drums is a so-called perforated drum.
An example of the previously mentioned friction spinning method and a spinning device in which a friction spinning drum is used has been disclosed in the commonly assigned European Published patent application No. 175,862. From that published patent application it is also apparent that the friction spinning means does not have to be in the form of a perforated drum; it could also, for instance, comprise a perforated disc combined with a conical roller.
Friction spinning devices using perforated drums or discs are known and are therefore not further described in this disclosure.
The purpose of the friction spinning device is to take up fibers fed to a fiber receiving surface of the perforated drum or disc in known manner by means of an air stream and to twist the fibers into a yarn or the like in the region of the convergent parts or zone of the two friction spinning drums or of a friction spinning disc and conical roller. The yarn is withdrawn in a direction extending substantially at right angles to the direction of rotation of the friction spinning drums.
Two perforated drums, as disclosed in the German Pat. No. 2,449,583, or one imperforate drum and one perforated drum, or an imperforate conical roller and a perforated disc, as disclosed in the aforementioned European Published patent application No. 175,862, can be used as friction spinning means or elements.
The airstream required for transporting the fibers is drawn by suction through the holes or perforations of the means of a suction nozzle located in the interior of the friction spinning drum or below the friction spinning disc. It is therefore clear that, on the one hand, the holes or perforations of this friction spinning means must have a cross-section or cross-sectional area in the narrowest section or region of each of the holes or perforations which, on the one hand, is so small that it substantially prevents take-up of too many fibers by these holes or perforations during deposition on the fiber receiving surface of the friction spinning means; such fibers may be either sucked away and lost, or at least cut on an edge of the mouth of the suction nozzle and thereby shortened.
On the other hand, the energy consumption of equipment of this kind should be held as low as possible, the quantity of air required making up a substantial part of the energy consumption. Furthermore, efforts should be made to oppose the tendency towards blockage of the holes or perforations. In friction spinning means of this kind, it is therefore desirable to select the hole or perforation section at the narrowest region or throat to be as large as possible from this viewpoint.
However, these requirements placed on the hole or 1 perforation diameter stand in direct opposition to each other.
From practical operation and from patent publications, for example, the German Published patent application No. 3,114,093, it is known that these holes or perforations, when formed with a circular cross-section or cross-sectional configuration, generally have a diameter between 0.5 and 0.8 mm.
On the other hand, the perforated drums must have inherent stiffness or rigidity so that no deformation arises in use. This calls for a minimum wall thickness of at least 1 mm when brass is used with, for example, a drum diameter of 50 mm.
It is, however, apparent that boring of such small holes or perforations, where the number of holes or perforations is in the region of several tens of thousands of holes or perforations per drum, in a material of 1.0 to 1.5 mm or greater thickness, cannot be carried out without problems and is therefore expensive.
If additional demands are placed upon the form or configuration of the holes or perforations, as in the case of German Published Pat. No. 2,919,316, then the manufacturer of such perforated drums is faced with special problems.